In semiconductor production, wafers are sequentially processed in a plurality of process steps during the production process, a plurality of identical repeating pattern elements being produced on one wafer. With increasing integration density, demands in terms of the quality of the features configured on the wafers are rising. To allow the quality of the configured features to be checked, and any defects to be found, requirements in terms of the quality, accuracy, and reproducibility of the components and process steps that handle the wafer are correspondingly high. This means that in the production of a wafer, with the many process steps and many layers of photoresist or the like to be applied, reliable and timely detection of defects in the individual features is particularly important.
A device for handling disk-shaped objects in a treatment plane of a local clean room is known, for example, from DE 43 10 149 C2. Here magazine receptacles are provided that are adjustable in elevation with respect to the treatment plane. Workstations for processing or inspection purposes are located in the treatment plane. The treatment plane is arranged above an intermediate floor that subdivides the clean room into two sub-spaces one above another, in which an air stream component of an air stream is directed out of the sub-space above the intermediate floor into the sub-room, containing the drive parts, below the intermediate floor. The air flow prevents any abraded material caused by the drive elements from traveling to the workstations in the treatment plane. The air preparation system comprises a housing, and its air outlet is constituted by a circle-sector-shaped cutout having air-directing panels.
It is advantageous, after each process step is performed, to check the quality achieved with that step. After lithography, for example, during the manufacturing process and even before any subsequent process step, the quality achieved in each case can be reliably evaluated. Thus, if a determination is made, just after a process step is performed and even before a production process has been completed, that a wafer or features configured on the wafer are defective, the wafer can be immediately discarded with no need to perform additional subsequent process steps. Or wafers found to be defective can be reprocessed separately until satisfactory quality is achieved. Efficiency and yield in semiconductor production can thereby be enhanced.
Optical apparatuses are particularly suitable for inspecting the surface of wafers. Examination of the surface can be accomplished, for example, as is known from EP 455 857, by evaluating beams that are retroreflected from the surface of the wafer.
Also known are optical apparatuses that, by image recognition, can recognize a wide variety of features on the surface of a wafer. The wafer is usually illuminated in bright-field fashion in this context, and scanned with a camera (matrix or linear camera).
One such inspection apparatus of KLA-Tencor Corporation is described in the article “Lithography Defects: Reducing and Managing Yield Killers Through Photo Cell Monitoring,” by Ingrid Peterson, Gay Thompson, Tony DiBiase, and Scott Ashkenaz, Spring 2000, Yield Management Solutions. The wafer inspection apparatus described therein operates with an incident-light illumination device that examines low-contrast microdefects using bright-field/dark-field illumination.
Defects on the wafer can be detected using bright-field and/or dark-field illumination, the radiation reflected respectively in diffuse or directional fashion from the wafer being evaluated. The radiation incident onto the wafer has a substantial influence on the reliability of the measurement result. If the illumination conditions change over time due a change in the adjustment of the lamp or because of aging effects in the illumination source, this can result in distorted or incorrect measurement results. In particular, defects can be simulated.